Palladium Catalyst in the HBIW Hydrodebenzylation Reaction. Deactivation and Spent Catalyst Regeneration Procedure

Abstract

The polycyclic nitramine 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12- hexaazaisowurtzitane (HNIW, CL-20) is synthesized via hydrodebenzylation of 2,4,6,8,10,12-hexabenzyl-2,4,6,8,10,12-hexaazaisowurtzitane (HBIW) over a palladium-based catalyst. This process is the key step in the synthesis of CL-20, a compound with unique energetic and explosive characteristics. The use of CL-20 is restricted at present by the high cost of the hydrodebenzylation process, during which the palladium-based catalyst becomes rapidly deactivated. The catalyst deactivation has now been shown to consist of deposition of the reaction products on the carbon support with simultaneous blocking of the active centers by these products. The HBIW decomposition products can permanently combine with palladium, thereby reducing the number of the active centers on the catalyst. Other byproducts clog the pores of the active carbon and reduce both the surface area of the active carbon and the pore volume. The reaction yield is also reduced by aggregation of palladium particles. A palladium catalyst regeneration procedure which has now been developed, consists of heating the catalyst for a specific time at 350 °C in a nitrogen and water vapour stream, and allows partial recovery of the activity of the palladium catalyst in a subsequent HBIW hydrodebenzylation reaction. The specific area and overall pore volume of the regenerated catalyst are also enhanced. The yield from the HBIW hydrodebenzylation reaction using the regenerated catalyst was ca. 42%